The aim of this project is to study the effects of selected drugs upon certain aspects of behavior in monkeys. Emphasis is placed upon the elucidation of pharmacological effects upon higher mental processes, particularly discrimination learning, perception, and complex behaviors. The tests used are modifications of some which have been shown to be sensitive to cerebro-cortical lesions in monkeys, plus other measures of choice behavior where the psychophysiological correlations are not yet so clear. A continuing effort is being made to improve methods of administering drugs to monkeys (e.g., inhalation methodologies) and to increase the efficiency with which complex functions will be investigated with the use of recently developed paradigms in the areas of attention, feature-selection learning, stimulus generalization, concept formation, and drug discrimination. In addition, previously developed tests and measures such as delayed response and delayed matching will be employed. Representative stimulant and depressant drugs have been intensively studied in both normal and brain lesioned animals. We propose to continue such investigations and expand our list of drugs to include hallucinogens and potent analgesics.